Components, Instances, and Elements | Lecture 121 | React.JS 🔥
Summary
TLDRThe video script delves into the conceptual differences between React components, component instances, and React elements. It explains that components are JavaScript functions that return React elements, serving as blueprints or templates for the UI. Component instances are the actual manifestations of these components, each holding its own state, props, and lifecycle. React elements, on the other hand, are immutable JavaScript objects created from component instances, containing information to generate DOM elements. The script highlights the journey from writing a component to rendering it as HTML in the DOM, clarifying the distinction between these key React concepts.
Takeaways
- 🔍 Components in React are essentially blueprints or templates for a piece of the UI, described using JSX syntax.
- 🛠️ A React component is a regular JavaScript function that returns React elements, forming an element tree.
- 🔄 Multiple instances of a component can be created from a single blueprint, each instance representing the component's physical presence in the component tree.
- 📦 Each component instance holds its own state and props, and goes through its own lifecycle, akin to a living organism.
- 🔄 Despite technical differences, the terms 'component' and 'component instance' are often used interchangeably in practice.
- 🔧 When a component is used in code, React elements are generated, which are immutable JavaScript objects kept in memory.
- 🔗 React elements contain all necessary information for creating DOM elements for the current component instance.
- 🎨 Ultimately, React elements are converted into actual DOM elements, which are then rendered to the screen by the browser.
- 🌐 The DOM elements are the final, visual representation of a component instance in the browser, not the React elements themselves.
- 🚀 The process from writing a component to it being rendered as HTML elements in the DOM illustrates the lifecycle of components in React applications.
Q & A
What is the conceptual difference between React components, component instances, and React elements?
-React components are the functions we write to describe a piece of the user interface, which return React elements. A component instance is the actual physical manifestation of a component in our componentry, created each time we use the component in our code. React elements are the immutable JavaScript objects created by calling React.createElement, containing information necessary to create DOM elements for the current component instance.
How are component instances created?
-React creates a new component instance each time we use the component in our code. For example, if a component is included three times in an app component, React will call the component function three times, creating three instances.
What does a component instance contain?
-Each component instance holds its own state, props, and lifecycle. It's like a living organism that can be born, live for some time, and eventually die.
What is the role of React elements?
-React elements are the result of using a component in our code. They are immutable JavaScript objects that React keeps in memory, containing information necessary to create DOM elements for the current component instance.
How are DOM elements created from React elements?
-React elements are not directly rendered to the DOM. Instead, they are converted to actual DOM elements, which are then painted onto the screen by the browser.
Can we use the terms 'component' and 'component instance' interchangeably?
-In practice, we often use the terms 'component' and 'component instance' interchangeably, even though 'component instance' would be more technically accurate when referring to the actual manifestation of a component in our componentry.
What is the purpose of JSX?
-JSX is a syntax extension that allows us to write React elements using a syntax that looks like HTML. Behind the scenes, JSX gets converted to multiple React.createElement function calls, which create the React elements.
What is the journey from writing a component to rendering it on the DOM?
-The journey starts with writing a component function, which is used multiple times in our code as a blueprint. Each time it is used, React creates a component instance, which returns a React element. This React element is then converted to actual DOM elements and painted onto the screen by the browser.
Why is understanding the difference between components, instances, and elements important?
-Understanding this difference is important because it helps clarify what actually happens with our components as we use them in our React applications. It's also a common interview question, so it's worth learning about this topic.
Can React elements directly influence the DOM?
-No, React elements themselves have nothing to do with the DOM. They simply live inside the React app and are used to create DOM elements when they are rendered on the screen.
Outlines
🧠 The Conceptual Differences Between React Components, Instances, and Elements
This paragraph explains the key differences between React components, component instances, and React elements. Components are JavaScript functions that describe a piece of the user interface by returning an element tree, typically using JSX syntax. Component instances are created when a component is used in the code, each with its own state, props, and lifecycle. React elements are immutable JavaScript objects containing the information needed to create DOM elements for a particular component instance. React elements are eventually converted to actual DOM elements and rendered in the browser. The paragraph emphasizes the journey from writing a component to rendering its instances as HTML elements in the DOM.
Mindmap
Keywords
💡React Components
💡Component Instances
💡React Elements
💡JSX
💡State
💡Props
💡Component Lifecycle
💡DOM Elements
💡Blueprint
💡Immutable
Highlights
Components are what we write to describe a piece of the user interface, and they are regular JavaScript functions that return React elements.
A component is a generic description of the UI, like a blueprint or template, while React creates one or multiple component instances from this blueprint.
Each component instance holds its own state, props, and lifecycle, and can be born, live for some time, and eventually die, like a living organism.
In practice, we often use the terms 'component' and 'component instance' interchangeably, even though 'component instance' is technically more accurate.
As React executes the code in each component instance, it returns one or more React elements.
A React element is basically the result of using a component in our code, and it's an immutable JavaScript object that React keeps in memory.
A React element contains all the information necessary to create DOM elements for the current component instance.
The React element is eventually converted to actual DOM elements and painted onto the screen by the browser.
The DOM elements are the final, visual representation of the component instance in the browser.
React elements live inside the React app and have nothing to do with the DOM directly. They are simply converted to DOM elements when rendered.
The journey starts from writing a single component, using it multiple times as a blueprint, converting it to a React element, and finally rendering it as HTML elements into the DOM.
The conceptual difference between React components, component instances, and React elements is explained.
Understanding this difference will help make it clearer what actually happens with components as they are used.
This topic is a common interview question and worth learning about.
The process of creating React elements using JSX behind the scenes is mentioned.
Transcripts
Let's start this section
with the conceptual difference between React components,
Component instances, and React elements.
Knowing about this difference will hopefully
make it a bit more clear what actually happens
with your components as you use them.
And also this is a pretty common interview question.
And so this topic is definitely worth learning about.
And let's begin by taking another look at components.
So components are what we write
in order to describe a piece of the user interface.
And the component is just a regular JavaScript function,
but it's a function that returns React elements.
So it returns an element tree.
And we usually write these elements using the JSX syntax.
Now a component is a generic description of the UI.
So we can essentially think of a component as a blueprint
or a template, and it's out of this one blueprint
or template that React then creates one
or multiple component instances.
Now, React does this each time that we use the component
somewhere in our code.
For example, the tap component that we saw
in the last slide is used, so it is included three times
in this app component.
And so therefore, three instances of tap are placed
in a component tree.
So in our actual application.
Behind the scenes, this happens
because React will call the tap function three times.
So one time for each instance.
So we can say that an instance is like the actual
physical manifestation of a component living
in our componentry.
While the component itself is really just a function
that we wrote before being called.
And actually, it's each instance
that holds its own state and props
and that also has its own life cycle.
So basically, a component instance can be born,
it can live for some time until it will eventually die.
So it's a bit like a living organism really.
Now in practice, we many times just use the terms component
and component instance interchangeably.
For example, we just say component life cycle
and not component instance life cycle.
And we also say that a UI is made up of components,
not of component instances,
even though instances
would technically be more accurate.
Okay, so just keep that in mind in the future
when you read documentation
or some stack overflow post or something like that.
But anyway, as React executes the code
in each of these instances,
each of them will return one or more React elements.
So as we learned when we first talked
about JSX behind the scenes, JSX will actually get converted
to multiple React.createElement function calls.
Then as React calls these create element functions
the result will be a React element.
So a React element is basically the result
of using a component in our code.
It's simply a big immutable JavaScript object
that React keeps in memory.
And we will take a look at this later in our account.
But what is this object actually?
Well, a React element basically contains all the information
that is necessary in order to create DOM elements
for the current component instance.
And so it's this React element that will eventually
be converted to actual DOM elements,
and then painted onto the screen by the browser.
So based on all this, the DOM elements are the actual, final
and visual representation
of the components instance in the browser.
And again, it's not React elements
that are rendered to the DOM.
React elements just live
inside the React app and have nothing to do with the DOM.
They are simply converted to DOM elements
when they are painted on the screen in this final step.
Okay, so this is the journey
from writing a single component to using it multiple times
in our code as a blueprint all the way
until it's converted to a React element,
and then rendered as HTML elements into the DOM.
So I hope you found this interesting and useful,
and if you did, then let's move on to the next video,
and take a look at all this in code.
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